chore: add undefined type to principalAccount

[dali546]

Reason for this change

When using TypeScript option exactOptionalPropertyTypes: truewe get the following error. All implementations ofIPrincipalhave the typestring | undefined` so this is change will apply it at the base

Type 'AccountPrincipal' is not assignable to type 'IPrincipal' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
  Types of property 'principalAccount' are incompatible.
    Type 'string | undefined' is not assignable to type 'string'.
      Type 'undefined' is not assignable to type 'string'.ts(2375)

Description of changes

Changed type definition of IPrincipal principalAccount

Describe any new or updated permissions being added

N/A

Description of how you validated changes

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.24%. Comparing base (48ae4d0) to head (dcda22d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #33055   +/-   ##
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  Coverage   82.24%   82.24%           
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  Files         119      119           
  Lines        6875     6875           
  Branches     1161     1161           
=======================================
  Hits         5654     5654           
  Misses       1118     1118           
  Partials      103      103           

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Components	Coverage Δ
packages/aws-cdk	∅ <ø> (∅)
packages/aws-cdk-lib/core	82.24% <ø> (ø)

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[lpizzinidev]

Hi @dali546 ✋
It seems that this PR raised a similar issue a while ago. The related discussion is still open.
I guess that general guidance should be provided for type declarations of | undefined / ?: props.
@kaizencc Thoughts?

[GavinZZ]

@lpizzinidev @dali546 thanks for the PR. I added some new update in the discussion post #23885 (comment).

Can you let me know your use case of the IPrincipal variable and if you can use the workaround mentioned. I'm happy to have this merged if the workaround mentioned does not work for you.

[dali546]

@GavinZZ the use case is even just creating simple roles using a principal, it causes the error eg

    const role = new Role(this, "role", {
      assumedBy: new WebIdentityPrincipal("accounts.google.com", {}),
    });

Type 'WebIdentityPrincipal' is not assignable to type 'IPrincipal' with 'exactOptionalPropertyTypes: true'. Consider adding 'undefined' to the types of the target's properties.
  Types of property 'principalAccount' are incompatible.
    Type 'string | undefined' is not assignable to type 'string'.
      Type 'undefined' is not assignable to type 'string'.ts(2375)

The proposed workaround of using the spread operator doesn't help here either because principalAccount? is defined inside WebIdentityPrincipal

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildv2Project1C6BFA3F-wQm2hXv2jqQv
• Commit ID: dcda22d
• Result: SUCCEEDED
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